1. Field of the Invention
This invention relates to heat-recoverable articles, more especially to such articles for use in protecting the ends of a length of cable, and to processes for their use.
2. Summary of the Prior Art
When electric cables, for example power or telecommunications cables, having a number of conductors surrounded by a jacket of insulating material are manufactured, they are frequently cut into lengths suitable for transport and storage on a former, for example a spool. The cut ends are protected against attack by water or other damaging media, and against mechanical injury by a covering which may be a wrapping of a tape or by a heat-shrinkable "end-cap".
The end cap is a generally tubular article, having one closed and one open end, which is capable of shrinking radially when heated above a certain temperature or temperature range. The article is made, for example, by moulding a thermoplastic composition containing a chemical crosslinking agent, in an appropriate shape having a diameter slightly smaller than the smallest diameter of cable in the range of sizes for which it is to be used. The crosslinked moulded article is then heated, expanded by air or mechanical pressure, cooled while maintaining the pressure, and then the pressure is released. In use, the article is placed over the end of the cable to be protected, and heated to cause it to shrink. The inner surface of the article may, if desired, be provided with a coating that assists in bonding the cap to substrate cable, and in preventing moisture ingress, for example a hot melt adhesive, or a non-crystalline layer of, for example, mastic.
Although the use of a heat-shrinkable "end-cap" has become accepted, there remains a problem, which is also present when other means of protecting cable ends, for example with tape-wrapping, are used, namely that during transport and storage of the capped cable, relative movement of the conductors and the insulating jacket (to which the end covering is firmly attached) tends to force the conductors through the closed end of the protective covering, allowing moisture ingress, etc.